The present invention is an improved cardioplegia delivery system for arresting the heart during cardiopulmonary bypass. During the cardiopulmonary bypass procedure, the patient's heart and lungs are supported by the cardiopulmonary bypass (CPB) machine (heart lung machine). It is necessary in many cases and desirable in some cases to completely arrest the beating of the heart in order to perform the heart surgery. For example a valve replacement surgery nearly always requires cessation of the beating heart since the heart chambers must be opened and the surgeon requires a clear, non-bloody field in which to work. During most coronary artery bypass graft (CABG) procedures, the surgeon may elect to arrest the heart and place the patient on the CPB machine in order to suture to a still, blood free coronary artery. This case is considered optional because some CABG's are done without arresting the heart but by stabilizing and immobilizing a portion of the heart upon which the surgeon desires to operate.
Cardioplegia is a common technique in cardiopulmonary bypass. Cardioplegia is a cold solution which is injected into the patient's coronary arteries. A key, active component of cardioplegia is potassium. The combination of potassium and cold (typically <10° C.) arrests the heart. The cardioplegia is typically injected in bolus' of approximately 200-400 cc. of fluid approximately every 15-20 minutes. A majority of surgeons elect to mix oxygenated blood from the heart lung machine into the cardioplegia and cool the mixture. The blood acts to nourish and oxygenate the patient's heart muscle or myocardium.
The current state of the art of myocardial protection which is another term for cardioplegia delivery, is to deliver the blood and drug either via two separately controllable roller pumps or via two tubes in the same roller pump raceway. A peristaltic roller pump is a positive displacement pump. It will displace a volume dictated by the relative volume of the tubing in the pump raceway. The volume of the tube in the raceway is defined by the equation:V=L*(π*d2/4)  eqn. 1
Where:
L=length of tubing in the pump raceway
π=pi
d=inner diameter of the plastic tubing
A majority of operations are done each year with cardioplegia delivered by the two tubes in a single raceway of a roller pump. It is the surgeons preference as to what ratio of blood and drug are mixed together. Less frequently, a dual head roller pump may be used to deliver the cardioplegic solution. In the case of two pump heads, the pumps can run at different rates and variable blood to drug ratios can be delivered. In the former case of a single pump raceway, the ratio of the two tubes determines the delivered mixture of blood vs. cardioplegic drug. For example, a popular ratio is four parts blood to one part drug. This is accomplished by a 0.25″ i.d. tube for the drug and a 0.125 inch i.d. tube for the drug. The ratio of the two volumes for a given identical length of tubing is four.
The conventional state of the art is there are multiple tubing sets sold with various blood to drug ratios. Popular options include 4:1 blood to drug, 2:1, 1:1, 8:1, etc. If multiple surgeons in the same hospital desire different myocardial protection protocols, the hospital must stock different part numbers.
The conventional state of the art in cardioplegia delivery involves cooling the mixture with a blood to water heat exchanger. Blood cardioplegia is pumped on one side of the heat exchanger while icy cold water is pumped on the other side of the heat exchanger. Heat is transferred from the blood into the water which cools the blood/drug mixture to a hypothermic temperature of 4-10° C.
Cardioplegia is typically delivered intermittently. For example, at the beginning of the bypass surgery, the surgeon may elect to arrest the heart with a large bolus of cardioplegia; for example 500-1,000 ml. Once the heart is arrested, it is desirable to turn off the cardioplegia so that blood does not continue to circulate through the patient's coronary arteries. As the surgeon is repairing a valve or sewing a bypass graft into a coronary artery, blood in the coronary arteries will diminish visualization of the surgical site. Since the cold, arrested heart requires much less oxygen and nutrients, the heart can stay dormant for 15-25 minutes between doses of cardioplegia with minimal ill effects. Typically a lower dose of cardioplegia is delivered every 10-20 minutes and the pump is turned off in between doses. Maintenance doses of cardioplegia after the initial arrest will range from 200-400 ml.
At the end of the surgery, the heart is typically warmed. A warm dose of cardioplegia is frequently given to transition the myocardial tissue from a cold, dormant state to warm and beating. Thus the cardioplegia delivery system should optimally both cool and warm the blood. This can be done by pumping either cold or warm water through the water to blood heat exchanger.
Another present convention in cardiopulmonary bypass equipment is to locate the heart lung machine remotely from the patient. Typically the patient's venous blood is drained from the venous side via large bore catheters inserted in the patient's right atrium and inferior vena cava. The blood is drained through approximately eight feet of plastic tubing (typically polyvinyl chloride or PVC) to the venous reservoir which collects the blood. Blood is pumped via either a roller pump or a centrifugal pump through an arterial heat exchanger which is used to cool the patient's systemic temperature. Blood passes out of the heat exchanger into the oxygenator which blows off carbon dioxide and adds oxygen to the blood. Blood exits the oxygenator/heat exchanger into eight feet of tubing to return blood to the patient's aorta.